A farm has chickens and rabbits. The number of chickens is four times the number of rabbits. They have 360 legs altogether. How many chickens are there?
Uncle An has a rectangular garden 9 m wide and 10 m long. He uses a corner for a pond as shown and grows vegetables in the rest. Find the vegetable area in $\mathrm{m}^2$. Take $\pi=22/7$.
Editorial interpretation of the drawing: the pond is a quarter-circle centered at the upper-left corner.
A square tile of side 20 cm has the pattern below, with four identical right-angled triangles and a small shaded square. Find the shaded area in $\mathrm{cm}^2$.